Addition-curable silicone gel composition

ABSTRACT

A silicone gel composition is characterized by excellent storage stability in a non-cured state and by high adhesion to a substrate and long-term stability of consistency at elevated temperatures after curing. The silicone gel composition comprises: a polyorganosiloxane (A), which consists of polyorganosiloxane (A-1) that contains R(CH 3 ) 2 SiO 2/2  units, RsiO 3/2  units, and R(CH 3 )  2 SiO 1/2  units, and polydiorganosiloxane (A-2) that contains R(CH 3 ) 2 SiO 2/2  units and R(CH 3 ) 2 SiO 1/2  units; a polyorganosiloxane (B), which contains in one molecule two silicon-bonded hydrogen atoms; an addition-reaction platinum catalyst (C); an organosilicon compound (D) selected from silane of the general formula (R 1 O) n SiR 2   4-n  or a partially hydrolyzed condensate thereof; and an organic titanium compound (E).

TECHNICAL FIELD

[0001] The present invention relates to an addition-curable silicone gelcomposition, in particular, to a silicone gel composition which ischaracterized by high storage stability, improved adhesion to asubstrate in a cured state, and capability of forming a silicone gelhaving consistency stable over a long period of time and under anelevated environmental temperature.

BACKGROUND ART

[0002] Due to good stress-relaxation, electrical, heat-resistant, andweather proof properties of cured compounds produced from silicone gelcompositions, these compositions find wide application for preparationof fillers and sealants used in electric and electronic devices. Anexample of such a silicone gel composition is the one having abranch-structured polyorganosiloxane having a molecular terminal cappedwith a silicon-bonded vinyl group, a polydiorganosiloxane having bothmolecular terminals capped with silicon-bonded vinyl groups, apolyorganosiloxane having silicon-bonded hydrogen atoms only on bothmolecular terminals, and a platinum catalyst (see Japanese PatentApplication Publication No. Sho 62-181357).

[0003] However, a silicone gel obtained by curing the aforementionedcomposition has poor adhesion to a substrate and can be easily peeledoff from the substrate under the effect of heat cycles and physicalstress. It has been proposed to overcome the above drawback by using asilicone gel composition improved either by adding siloxane units havingalkoxy or epoxy groups to the base polymer or to a cross-linking agent(see Japanese Patent Application Publication No. Hei 4-88060). Anothermethod is based on the use of a silicone gel composition based on theaddition of an aluminum organic compound and an alkoxyalkyl silanecompound to a specific polyorganosiloxane compound (see Japanese PatentApplication Publication No. Hei 6-107947), or on the use of apolyorganosiloxane composition that contains a chain extender having inone molecule two silicon-bonded hydrogen atoms, a cross-linking agentwith at least three silicon-bonded hydrogen atoms in one molecule, analkylpolysilicate, and an alkyl titanate (see Japanese PatentApplication Publication No. Hei 7-233326).

[0004] However, improvement achieved in thermal stability and inadhesion of a silicone gel obtained by curing the above composition to asubstrate is not sufficient, and when such silicone gel is maintainedover a long period of time at relatively high temperatures that exceed180° C., it begins to lose its consistency, i.e., becomes harder, caneasily be peeled off the substrate, and forms “cracks” in the gel.Furthermore, if a silicone gel composition contains an organoaluminumcompound, long-term storage of this composition prior to curing causesprecipitation and separation of the organoaluminum compound.

DISCLOSURE OF INVENTION

[0005] The inventors carried out a study aimed at the solution of theproblems associated with this technique. As a result of this study, theyarrived at the present invention. More specifically, it is an object ofthe present invention to provide a silicone gel composition, which ischaracterized by excellent storage stability in a non-cured state and bystrong adhesion to a substrate and by long-term stability of consistencyat elevated temperatures after curing.

[0006] The present invention provides a silicone gel composition whichcomprises:

[0007] 100 parts by weight of a polyorganosiloxane (A), which has aviscosity from 10 to 100,000 mPa·s at 25° C. and contains 20 to 100 wt.% polyorganosiloxane (A-1) that contains 80.0 to 99.8 mole % ofR(CH₃)SiO_(2/2) units, 0.1 to 10.0 mole % of RSiO_(3/2) units, and 0.1to 10.0 mole % of R(CH₃)₂SiO_(1/2) units (where R is a monovalenthydrocarbon and where alkenyl groups constitute 0.25 to 4.0 mole % ofthe entire R), and 0 to 80 wt. % polydiorganosiloxane (A-2) thatcontains 90.0 to 99.9 mole % of R(CH₃)SiO_(2/2) units and 0.1 to 10.0mole % of R(CH₃)₂SiO_(1/2) units (where R is a monovalent hydrocarbonand where alkenyl groups constitute 0.25 to 4.0 mole % of the entire R);

[0008] a polyorganosiloxane (B), which has a viscosity from 2 to 10,000mPa·s at 25° C. and contains in one molecule at least two silicon-bondedhydrogen atoms, the aforementioned polyorganosiloxane (B) being used insuch an amount that a mole ratio of silicon-bonded hydrogen atomscontained in this component is within the range of 0.8 to 1.2 relativeto the amount of alkenyl groups in component (A);

[0009] an addition-reaction platinum catalyst (C) used in such an amountthat in terms of weight units the metallic platinum constitutes 0.01 to1000 ppm per total weight of components (A) and (B);

[0010] 0.05 to 20 parts by weight of an organosilicon compound (D)selected from a silane of the general formula (R¹O)_(n)SiR² _(4-n) and apartially hydrolyzed condensate thereof (in the aforementioned formula,R¹ is a alkyl or an alkoxyalkyl group, R² is a substituted ornon-substituted monovalent hydrocarbon group, and “n” is 3 or 4); and

[0011] 0.001 to 5 parts by weight of an organic titanium compound (E),wherein none of the polyorganosiloxane, except for component (B),contains silicon-bonded hydrogen atom;

[0012] the aforementioned silicone gel composition having a cured-state¼ consistency, as specified by JIS K 2220, within the range of 10 to200.

[0013] The silicone gel composition of the present invention will befurther described in more detail.

[0014] A polyorganosiloxane (A) is the main component of the compositionof the invention. This component contains 20 to 100 wt. %polyorganosiloxane (A-1) containing R(CH₃)SiO_(2/2) units, RSiO_(3/2)units, and R(CH₃)₂SiO_(1/2) units and 0 to 80 wt. % polydiorganosiloxane(A-2) containing R(CH₃)SiO_(2/2) units and R(CH₃)₂SiO_(1/2) units. Ifthe content of constituent (A-1) is less then 20 wt. %, the obtainedcomposition might not cure sufficiently. If necessary, the entirecomponent (A) may consist of constituent (A-1). It is recommended forcomponent (A) to have viscosity of 10 to 100,000 mPa·s. If viscosity isbelow the lower limit of the aforementioned range, the compositioneither will become too fluid in a non-cured state, or will acquireinsufficient physical properties after curing. In case the viscosityexceeds the upper limit, the composition will become difficult to handleand degas during production.

[0015] Constituent (A-1) contains R(CH₃)SiO_(2/2), RSiO_(3/2), andR(CH₃)₂SiO_(1/2) units. Constituent (A-1) may contain only theaforementioned three units. If necessary, however, one or two, or morethan two of the following other units can be added to this constituentin small quantities: HO(CH₃)₂SiO_(1/2), RO(CH₃)₂SiO_(1/2),HO(CH₃)SiO_(2/2), and RO(CH₃)SiO_(2/2). In the above formulae, R is amonovalent hydrocarbon that can be represented by methyl, ethyl, propyl,butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, octadecyl or similaralkyl groups; cyclopentyl, cyclohexyl, or similar cycloalkyl groups;phenyl, tolyl, xylyl, naphthyl, or similar aryl groups; benzyl,phenethyl, phenylpropyl, or similar aralkyl groups; 3-chloropropyl,3,3,3-trifluoropropyl, or similar halogenated alkyl groups. Preferableamong these are methyl and phenyl groups. Alkenyl groups shouldconstitute 0.25 to 4.0 mole % of the entire R. If the amount of alkenylgroups in R is below the recommended lower limit, the obtainedcomposition will not possess sufficient curability. If, on the otherhand, the amount of alkenyl group exceeds the upper limit, it would bedifficult to produce a cured body in a gel-like state. The following areexamples of recommended alkenyl groups: a vinyl, allyl, butenyl,pentenyl, or a hexenyl group. Most preferable is a vinyl group.

[0016] It is recommended that constituent (A-1) contain 80.0 to 99.8mole % of R(CH₃)SiO_(2/2) units, 0.1 to 10.0 mole % of RSiO_(3/2) units,and 0.1 to 10.0 mole % of R(CH₃)₂SiO_(1/2) units. If the content ofRSiO_(3/2) units is below the lower limit of the recommended range, itwould be difficult to cure the composition to a sufficient degree. Ifthe content of these units exceeds the upper limit of the range, theobtained composition will become too viscous and will possess lowflowability. Although there are no special limitations with regard toviscosity of constituent (A-1), it is preferable if viscosity of thisconstituent is within the range of 10 to 10,000 mPa·s.

[0017] Constituent (A-2) is a polydiorganosiloxane which containsR(CH₃)SiO_(2/2) units and R(CH₃)₂SiO_(1/2) units. This constituent maycontain only the aforementioned two groups. If necessary, however, oneor two, or more than two of the following other units can be added tothis constituent in small quantities: HO(CH₃)₂SiO_(1/2),RO(CH₃)₂SiO_(1/2), HO(CH₃)SiO_(2/2), and RO(CH₃)SiO_(2/2). In theseformulae, R has the same meaning as defined earlier. It is recommendedthat constituent (A-2) contain 90.0 to 99.9 mole % of R(CH₃)SiO_(2/2)units and 0.1 to 10.0 mole % of R(CH₃)₂SiO_(1/2) units. Although thereare no special limitations with regard to viscosity of constituent(A-2), it is preferable if viscosity of this constituent is within therange of 100 to 100,000 mPa·s.

[0018] Polyorganosiloxane of component (B) is used for cross-linking andcuring of the composition of the invention into a gel-like substance dueto hydrosilation reaction. Component (B) is characterized by having twosilicon-bonded hydrogen atoms in one molecule. If the number ofsilicon-bonded hydrogen atoms in one molecule is less than 2, theobtained silicone gel composition will not possess sufficientcurability, and after curing it could be easily peeled off from asubstrate. If, on the other hand, the number of silicon-bonded hydrogenatoms exceeds 2, the silicone gel obtained after curing the silicone gelcomposition of the invention will have low resistance to heat.

[0019] Component (B) may have a linear, partially-branched linear,branched, cyclic, or resin-like molecular structure. Hydrogen atoms canbe bonded to silicon at molecular terminals or at sides of the molecularchain. Apart from hydrogen atoms, the following organic groups can bebonded to silicon atoms in component (B): methyl, ethyl, propyl, butyl,pentyl, hexyl, heptyl, octyl, nonyl, decyl, octadecyl or similar alkylgroups; cyclopentyl, cyclohexyl, or similar cycloalkyl groups; phenyl,tolyl, xylyl, naphthyl, or similar aryl groups; benzyl, phenethyl,phenylpropyl, or similar aralkyl groups; 3-chloropropyl,3,3,3-trifluoropropyl, or similar halogenated alkyl groups. Preferableamong these are methyl groups and phenyl groups.

[0020] It is recommended for component (B) to have viscosity within therange of 2 to 10,000 mPa·s at 25° C. Viscosity at 25° C. below the lowerlimit will impair storage stability and handling of the compositionunder industrial conditions. On the other hand, if viscosity exceeds theupper limit, this also will impair handling of the composition duringuse in the production process. Component (B) can be represented by acopolymer of a methylhydrogensiloxane and a dimethylsiloxane having bothmolecular terminals capped with trimethylsiloxy groups, adimethylpolysiloxane having both molecular terminals capped withdimethylhydrogensiloxy groups, a polyorganosiloxane that consists of(CH₃)₃SiO_(1/2), (CH₃)₂ HSiO_(1/2), and SiO_(4/2), units, apolyorganosiloxane that consists of (CH₃)₃ SiO_(1/2), (CH₃)₂ HSiO_(1/2),(CH₃)₂ SiO_(2/2), and SiO_(4/2) units, or mixtures of the aforementionedpolyorganosiloxanes. Most preferable among the above is adimethylsiloxane having both molecular terminals capped withdimethylhydrogensiloxy groups.

[0021] It is recommended that component (B) be used in such an amountthat a mole ratio of silicon-bonded hydrogen atoms contained in thiscomponent is within the range of 0.8 to 1.2, preferably 0.9 to 1.1,relative to the amount of silicon-bonded alkenyl groups in component(A). If the aforementioned mole ratio of silicon-bonded hydrogen amountsin component (B) to silicon-bonded alkenyl groups in component (A) isbelow the minimal limit of the above range, either the obtainedcomposition will not be sufficiently curable and will not exhibitsufficient viscosity during curing, or the silicone gel obtained aftercuring will not possess sufficient adhesion to the substrate. In bothcases, the silicone gel obtained after curing will have low thermalstability.

[0022] Component (C) is an addition-reaction platinum catalyst intendedto promote addition of silicon-bonded hydrogen atoms of component (B) tosilicon-bonded alkenyl groups of component (A). This platinum catalystcan be represented by a platinum black, platinum-carrying activatedcarbon, platinum-carrying fine silica powder, chloroplatinic acid, analcoholic solution of chloroplatinic acid, a platinum-olefin complex, aplatinum-alkenylsiloxane complex, and a fine thermoplastic resin powderthat contains a platinum-type catalyst. The aforementioned thermoplasticresin may comprise a silicone resin, polycarbonate resin, acryl resin,nylon resin, or a polyester resin. It is recommended that theaforementioned resin have a softening point of 5 to 200° C. and havediameter of particles within the range of 0.01 to 10 micrometers.

[0023] It is recommended to use component (C) in such an amount that interms of weight units the metallic platinum constitutes 0.01 to 1000ppm, preferably 0.1 to 100 ppm, per total weight of components (A) and(B). If the amount is below the lower limit, the obtained compositionwill not be sufficiently curable. If the amount of the catalyst exceedsthe recommended upper limit, the use of the surplus will not practicallyaccelerate the curing procedure and will not be justifiableeconomically.

[0024] Organosilicon compound (D) selected from silane of the generalformula (R¹O)_(n)SiR² _(4-n), or a partially hydrolyzed condensatethereof, is needed for improving adhesion of the silicone gel producedby curing to a substrate. In the aforementioned formula, R¹ is a alkylor an alkoxyalkyl group, R² is a substituted or non-substitutedmonovalent hydrocarbon group, and “n” is 3 or 4. Alkyl groups designatedby R¹ can be the same or different and can have 1 to 4 carbon atoms.Alkyl groups are represented by methyl groups, ethyl groups, or propylgroups. An example of an alkoxyalkyl group designated by R¹ ismethoxyethyl. Monovalent hydrocarbon groups represented by R² can berepresented by methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl,octyl, nonyl, decyl, octadecyl or similar alkyl groups; cyclopentyl,cyclohexyl, or similar cycloalkyl groups; phenyl, tolyl, xylyl,naphthyl, or similar aryl groups; benzyl, phenethyl, phenylpropyl, orsimilar aralkyl groups; 3-chloropropyl, 3,3,3-trifluoropropyl, orsimilar halogenated alkyl groups. Preferable among these are alkylgroups having 1 to 4 carbon atoms, 3,3,3-trifluoropropyl, or phenylgroup, but most preferable are methyl groups.

[0025] The aforementioned partially hydrolyzed condensate of silane mayhave a linear, branched, cyclic, or net-like molecular structure.Furthermore, it can be a monomer or a copolymer. The aforementionedpartially hydrolyzed condensate of silane can be represented by thefollowing general formula: (R¹O)_(2 (m+))Si_(m)O_(m−1), wherein R¹ isthe same as defined above, and m is an integer from 2 to 20. Thiscomponent should have viscosity of 0.1 mPa·s to 100 mPa·s at 25° C.

[0026] It is recommended to use component (D) in an amount of 0.05 to 20parts by weight, preferably 0.1 to 100 parts by weight, and even morepreferably 0.2 to 2 parts by weight, per 100 parts by weight ofcomponent (A). If component (D) is used in an amount that is below thelower limit, the cured silicone gel will not exhibit sufficient adhesionto the substrate. If the content of component (D) exceeds therecommended upper limit, either the composition will not have storagestability, or the silicone gel obtained after curing will haveunattractive appearance.

[0027] Organic titanium compound (E) protects the silicone gel from adecrease in thermal stability, which may be caused by addition ofcomponent (D). The following are examples of component (E): tetrabutyltitanate, tetraisopropyl titanate, tetraoctyl titanate, tetraphenyltitanate, or a similar organic titanic acid ester; diisopropoxy-bis(acetylacetonate) titanium, diisopropoxy-bis (ethylacetoacetate)titanium, or a similar organic titanium chelate.

[0028] It is recommended that component (E) be used in an amount of0.001 to 5 parts by weight, preferably 0.01 to 1 part by weight per 100parts by weight of component (A). If component (E) is used in an amountless than the lower limit of the above range, the silicone gel obtainedafter curing will not acquire sufficient thermal resistance. Ifcomponent (E) is used in an amount exceeding the recommended upperlimit, the obtained silicone gel will lose its storage stability.

[0029] In order to improve handling of the composition of the inventionunder industrial conditions, some additional components can be added tothis composition. The following addition reaction inhibitors areexamples of such additional components: 3-methyl-1-butyn-3-ol,3,5-dimethyl-1-hexyn-3-ol, 3-phenyl-1-butyn-3-ol, or a similaracetylene-type compound, 3-methyl-3-penten-1-yl,3,5-dimethyl-3-hexen-1-yl, or a similar enyne compound;1,3,5,7-teramethyl-1,3,5,7-tetravinyl cyclotetrasiloxane,1,3,5,7-tetramethyl-1,3,5,7-tetrahexenyl cyclotetrasiloxane, or asimilar cycloalkenyl siloxane; benzotriazole, or a similar triazolecompound. It is recommended that such inhibitors being used in an amountof 0.001 to 5 parts by weight per 100 pats by weight of component (A).

[0030] If necessary, the silicone gel composition of the invention cancontain other additives used in quantities not detrimental to thepurposes of the present invention. Examples of such additives are thefollowing: dry-process fine silica powder, wet-process fine silicapowder, fine quartz powder, fine powder of calcium carbonate, finepowder of titanium dioxide, fine powder of diatomaceous earth, finepowder of aluminum oxide, fine powder of aluminum hydroxide, fine powderof zinc oxide, fine powder of zinc carbonate, or a similar inorganicfiller; the aforementioned powdered fillers surface-treated with thefollowing substances: methyltrimethoxysilane,vinyltrimethoxyethoxysilane, or a similar organoalkoxysilane;trimethylchlorosilane or a similar organohalosilane;hexamethyldisilazane, or a similar organosilazane; dimethylsiloxaneoligomer having both molecular terminals capped with hydroxyl groups,methylphenylsiloxane oligomer having both molecular terminals cappedwith hydroxyl groups, methylvinylsiloxane oligomer having both molecularterminals capped with hydroxyl groups, or similar siloxane oligomers;higher fatty acids, or their metal salts. The composition of theinvention may contain also toluene, xylene, acetone, methylethylketone,methylisobutylketone, hexane, heptane, or a similar organic solvent;polydimethylsiloxane having both molecular terminals capped withtrimethylsiloxy groups, polymethylphenylsiloxane having both molecularterminals capped with trimethylsiloxy groups, or a similarnon-cross-linkable polyorganosiloxane; flame-retarding agents,heat-resistant agents, plasticizers, agents for imparting thixotropicproperties, adhesion enhancing agents, anticorrosive agents, pigments,dyes, fluorescent dyes, etc.

[0031] The silicone gel composition of the invention is prepared byuniformly mixing aforementioned components (A) to (E). The silicone gelcomposition of the invention can be stored in the form of two liquidsubcompositions, i.e., a first liquid subcomposition (I) consisting ofcomponents (A), (C), and (E), i.e., without components (B) and (D), anda second liquid subcomposition (II) consisting of components (A), (B)and (D), i.e., without components (C) and (E) {component (A) can bepresent in both liquid mixtures}. Prior to use, the aforementionedliquid subcompositions should be uniformly mixed. If necessary, thesilicone gel composition of the invention can be stored in the form of asingle liquid composition, but storing in the aforementioned two-liquidform provides better protection against curing during storage andagainst deterioration of adhesive properties.

[0032] The silicone gel composition of the invention should have acured-state ¼ consistency, as specified by JIS K 2220, within the rangeof 10 to 200, preferably within the range of 20 to 150. If thischaracteristic is below the lower limit of the above range, the siliconegel obtained from the composition will exhibit a decrease instress-relaxation properties and will be prone to formation of “cracks”.If, on the other hand, the cured-state ¼ consistency exceeds the upperlimit of the recommended range, the silicone gel will become flowableunder the effect of vibrations.

[0033] There are no special limitations with regard to the proceduresuitable for curing the silicone gel composition of the presentinvention. For example, the composition can be poured into anappropriate form or spread over the surface of a substrate as a coatingand cured by retaining it at room temperature, or by heating at 50° C.to 200° C.

[0034] The silicone gel composition of the invention is normally used asa filler or sealant for electrical and electronic devices of highreliability. In particular, the silicone gel composition of theinvention exhibits excellent adhesion to the materials: gold, silver,copper, nickel, aluminum, or similar metals used for manufacture ofelectrodes; poly-phenylene sulfide (PPS), polybutyleneterephthalate(PBT), or other engineering plastics used for manufacture of cases;epoxy resin, polyimide resin or similar thermosetting resins used formanufacture of printed circuit boards; ceramics such as alumina, aluminanitride, or the like; and substrates from various materials.

BEST MODE FOR CARRYING OUT THE INVENTION

[0035] The silicone gel composition of the invention will be describedin detail with reference to practical examples. Viscosity given in theseexamples relates to values at 25° C. Furthermore, the following methodswere used for measuring adhesion strength, cured-state ¼ consistency,and heat-resistant properties of the silicone gel composition of theinvention.

[0036] Adhesion Strength of Silicone Gel

[0037] A specimen for adhesion strength test was prepared by arrangingtwo 100-mm long, 25-mm wide, and 1-mm thick plates parallel to eachother, spacing them so that, after filling with the silicone gelcomposition, the layer formed by the composition was 25 mm long, 10 mmwide, and 1 mm thick, and curing the layer for 60 min. at 70° C.Adhesion strength was measured by stretching the obtained specimen at arate of 5 mm/min. in a direction perpendicular to the adhered surfaces.

[0038] Cured-state ¼ Consistency

[0039] A silicone gel composition was slowly poured into a 50 ml glassflask and formed into a silicone gel by heating for 1 hour at 70° C.Cured-state ¼ consistency of the obtained gel was measured in accordancewith the provisions of JIS K 2220.

[0040] Thermal Resistance of Silicone Gel

[0041] A silicone gel obtained after curing by the method describedabove was retained in an oven for 400 hours at 200° C. and then removedand cooled to 25° C. at room temperature. After such treatment,cured-state ¼ consistency of the gel was measured in accordance with theprovisions of JIS K 2220.

[0042] Practical Examples 1 to 3, Comparative Example 1 to 7

[0043] Components shown in Table 1 (in parts by weight) were uniformlymixed and produced in the form of 10 different silicone gelcompositions. These silicone gel compositions were retained intact for 3days at 5° C. and then checked with regard to storage stability byobserving formation of a precipitate. In addition to storage stability,the composition was tested with regard to adhesion strength, cured-state¼ consistency, and resistance to heat.

[0044] In the attached table, SiH/SiCH═CH₂ is presented in terms of amole number of silicon-bonded hydrogen atoms contained in component(b-1) or/and component (b-2) in a ratio to 1 mole of vinyl groups incomponents (a-1), (a-2) or/and (a-3).

[0045] Component (a-1) is a polyorganosiloxane (with 0.23 wt. % of vinylgroups) having viscosity 680 mPa·s and consisting of 93.5 mole %(CH₃)₂SiO_(1/2) units, 3.3 mole % CH₃SiO_(3/2) units, 2.3 mole %(CH₃)₃SiO_(1/2) units, and 0.9 mole % (CH₃)₂ (CH₂═CH) SiO_(1/2) units.

[0046] Component (a-2) is a 400 mPa·s viscosity dimethylpolysiloxanehaving both molecular terminals capped with dimethylvinylsiloxy groups(0.41 wt. % of vinyl groups) and consisting of 98.5 mole %(CH₃)₂SiO_(2/2) units and 1.5 mole % (CH₃)₂ (CH₂═CH) SiO_(1/2) units.

[0047] Component (a-3) is a 800 mPa·s viscosity dimethylpolysiloxanehaving both molecular terminals capped with trimethoxysiloxy groups andconsisting of 98.9 mole % (CH₃)₂SiO_(2/2) units and 1.1 mole %(CH₃O)₃SiO_(1/2) units.

[0048] Component (b-1) is a 16 mPa·s viscosity dimethylpolysiloxanehaving both molecular terminals capped with dimethylhydrogensiloxygroups (0.13 wt. % content of silicon-bonded hydrogen).

[0049] Component (b-2) is a 4 mPa·s viscosity copolymer of amethylhydrogensiloxane and a dimethylsiloxane having both molecularterminals capped with trimethylsiloxy groups (0.78 wt. % content ofsilicon-bonded hydrogen).

[0050] Component (c) is a complex of platinum with1,3-divinyl-1,1,3,3-tetramethyldisiloxane with 5 wt. % of metallicplatinum (2.48% content of vinyl groups).

[0051] Component (d-1) is an ethylpolysilicate [general molecularformula Si_(m)O(_(m−1))(OC₂H₅)₂(_(m+1)) where an average value of “m” is5), 40 wt % content of SiO₂, viscosity 5 mPa·s].

[0052] Component (d-2) is methyltrimethoxysilane.

[0053] Component (e-1) is diisopropoxy bis(ethylacetoacetate) titanium.

[0054] Component (e-2) is tetrabutyltitanate.

[0055] Component (e-3) is aluminum acetylacetonate. TABLE 1 PracticalExamples Comparative Examples 1 2 3 1 2 3 4 5 6 7 Composition Component(a-1) 50 100 100 50 50 50 50 50 50 — (parts Component (a-2) 50 — — 50 2550 50 50 50 100 by Component (a-3) — — — — 25 — — — — — weight)Component (b-1) 9.3 6.5 6.5 9.4 6.3 9.5 9.6 9.7 9.8 6.3 Component (b-2)— — — — — — — — — 0.6 Component (c) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.10.1 Component (d-1) 0.5 0.5 — — — 0.5 0 0.01 0.5 0.5 Component (d-2) — —0.5 — — — — — — — Component (e-1) 0.02 0.02 — — — — 0.02 0.02 — 0.02Component (e-2) — — 0.02 — — — — — — — Component (e-3) — — — — — 0.05 —— — — SiH/SiCH═CH₂ 0.99 0.99 0.99 1.00 0.99 1.01 1.02 1.03 1.04 0.81Adhesive Copper 200 190 175 80 150 200 75 80 180 180 Strength Nickel 190180 185 50 120 160 55 50 130 130 (gf) Polybutyleneterephthalate 175 165190 40 100 150 45 50 140 140 resin Alumina plate 220 210 215 170 195 210190 180 195 195 Resistance Cured-state 1/4 60 70 72 60 96 63 64 65 62 70to consistency in initial heat period Cured-state 1/4 58 68 68 55 20 2055 58 10 10 consistency after 200° C. × 500 hrs Storage Existence ofprecipitation No No No No No Yes No No No No Stability

[0056] Thus it has been shown that the gel composition of the presentinvention exhibits excellent stability in storage, and the silicone gelobtained by curing the composition has good adhesion to varioussubstrates and preserves its cured-state ¼ consistency over a longperiod of time even under elevated temperatures.

1. A silicone gel composition comprising: 100 parts by weight of apolyorganosiloxane (A) having a viscosity from 10 to 100,000 mPa·s at25° C., where polyorganosiloxane (A) comprises 20 to 100 wt. %polyorganosiloxane (A-1) that contains 80.0 to 99.8 mole % ofR(CH₃)SiO_(2/2) units, 0.1 to 10.0 mole % of RSiO_(3/2) units, and 0.1to 10.0 mole % of R(CH₃)₂SiO_(1/2) units, where R is a monovalenthydrocarbon and where alkenyl groups comprise 0.25 to 4.0 mole % of R,and 0 to 80 wt. % polydiorganosiloxane (A-2) that contains 90.0 to 99.9mole % of R(CH₃)SiO_(2/2) units and 0.1 to 10.0 mole % ofR(CH₃)₂SiO_(1/2) units; a polyorganosiloxane (B), which has a viscosityfrom 2 to 10,000 mPa·s at 25° C. and contains in one molecule twosilicon-bonded hydrogen atoms, said polyorganosiloxane (B) being used inan amount such that a mole ratio of silicon-bonded hydrogen atomscontained in component (B) is within the range of 0.8 to 1.2 relative toamount of alkenyl groups in component (A); an addition-reaction platinumcatalyst (C) used in such an amount that in terms of weight units themetallic platinum constitutes 0.01 to 1000 ppm per total weight ofcomponents (A) and (B); 0.05 to 20 parts by weight of an organosiliconcompound (D) selected from a silane of the general formula (R¹O)_(n)SiR²_(4-n) and a partially hydrolyzed condensate thereof, where R¹ is analkyl or an alkoxyalkyl group, R² is a substituted or non-substitutedmonovalent hydrocarbon group, and n is 3 or 4; and 0.001 to 5 parts byweight of an organic titanium compound (E); wherein none of thepolyorganosiloxanes, except for component (B), contains silicon-bondedhydrogen atom; said silicone gel composition having a cured-state ¼consistency, as specified by JIS K 2220, within the range of 10 to 200.2. The silicone gel composition of claim 1, wherein component (D) is analkyl silicate or alkyl polysilicate.
 3. The silicone gel composition ofclaim 1, wherein component (E) is an organic titanic acid ester or atitanium chelate.
 4. The silicone gel composition of claim 1, whereinpolyorganosiloxane (A-1) further comprises HO(CH₃)₂SiO_(1/2),RO(CH₃)₂SiO_(1/2), HO(CH₃)SiO_(2/2), or RO(CH₃)SiO_(2/2) units.
 5. Thesilicone gel composition of claim 1, wherein the monovalent hydrocarbonfor R comprises methyl and phenyl groups.
 6. The silicone gelcomposition of claim 1, wherein the alkenyl group for R is vinyl.
 7. Thesilicone gel composition of claim 1, wherein polydiorganosiloxane (A-2)further comprises HO(CH₃)₂SiO_(1/2), RO(CH₃)₂SiO_(1/2),HO(CH₃)SiO_(2/2), or RO(CH₃)SiO_(2/2) units.
 8. The silicone gelcomposition of claim 1, wherein component (B) is selected from the groupconsisting of a copolymer of a methylhydrogensiloxane and adimethylsiloxane having both molecular terminals capped withtrimethylsiloxy groups, a dimethylpolysiloxane having both molecularterminals capped with dimethylhydrogensiloxy groups, apolyorganosiloxane comprising (CH₃)₃SiO_(1/2), (CH₃)₂ HSiO_(1/2), andSiO_(4/2), units, a polyorganosiloxane comprising (CH₃)₃ SiO_(1/2),(CH₃)₂ HSiO_(1/2), (CH₃)₂ SiO_(2/2), and SiO_(4/2) units, and mixturesthereof.
 9. The silicone gel composition of claim 1, wherein the amountof component (B) is such that a mole ratio of silicon-bonded hydrogenatoms contained in this component is within the range of 0.9 to 1.1,relative to the amount of silicon-bonded alkenyl groups in component(A).
 10. The silicone gel composition of claim 1, wherein component (C)is selected from the group consisting of platinum black,platinum-carrying activated carbon, platinum-carrying fine silicapowder, chloroplatinic acid, an alcoholic solution of chloroplatinicacid, a platinum-olefin complex, a platinum-alkenylsiloxane complex, anda fine thermoplastic resin powder that contains a platinum-typecatalyst.
 11. The silicone gel composition of claim 1, wherein theamount of component (C) is 0.1 to 100 ppm, per total weight ofcomponents (A) and (B).
 12. The silicone gel composition of claim 1,wherein the amount of organosilicon compound (D) is 0.1 to 10 parts byweight per 100 parts by weight of component (A).
 13. The silicone gelcomposition of claim 1, wherein component (E) is an organic titanic acidester or an organic titanium chelate.
 14. The silicone gel compositionof claim 1, wherein the amount of component (E) is 0.01 to 1 part byweight per 100 parts by weight of component (A).
 15. The silicone gelcomposition of claim 1, further comprising an addition reactioninhibitor, an inorganic filler, an organic solvent; a non-cross-linkablepolyorganosiloxane, a flame-retarding agent, a heat-resistant agent, aplasticizer, an agent for imparting thixotropic properties, an adhesionenhancing agent, an anticorrosive agent, a pigment, a dye, a fluorescentdye, or combinations thereof.
 16. The silicone gel composition of claim1, wherein the composition comprises: (I) a first subcompositionconsisting of component (A), component (C), and component (E) and (II) asecond subcomposition consisting of component (A), component (B), andcomponent (D).